What the Hell is a Theory, Anyway?

I’m sure you’ve heard this classic one-liner from the creationist playbook: “Evolution is just a theory.” It makes me cringe every time I hear it, partly because I myself once used it on a classroom full of students. If only I could go back in time and smack that little twerp.

(Note: I know most of my readers are already familiar with the correct usage of the word theory, but I want to get this off my chest.)

What if I told you, “Einstein’s theory of relativity is just a theory”? Here’s how our conversation might go:

You: But it’s been proven.Me: No it hasn’t. Have you ever measured the speed of light?You: No, but scientists have.Me: No they haven’t. Did you know neutrinos move faster than light?You: But you just said… nevermind. That claim was debunked, anyway.Me: No it wasn’t. And if relativity is true, then morality is relative.You: Those are two completely unrelated topics.Me: No they’re not. Did you know Einstein believed in God?You: That has nothing to do with it. And that’s just a rumor, anyway.Me: No it isn’t. Besides, the theory of relativity is just a theory.

And on and on it goes. This is exactly what it’s like debating young earth creationists, and it makes me want to bang my head against the wall. They ask irrelevant questions like “were you there?“, they cite supposed contrary evidence that has been debunked, they bring up unrelated topics like morality (as if that could disprove the science), they tell lies about Darwin (which have nothing to do with his ideas), and worst of all: they say evolution is just a theory. Ugh.

I suppose no one will ever put this fallacy to rest, but I’m going to try anyway. Evolution is not just a theory! Evolution is a fact, and the theory of evolution by natural selection is the best explanation we have for that fact.

Have you ever looked up a word in the dictionary and noticed it has more than one definition? Oftentimes, two of the definitions are very different. For example, “light” could refer to how little something weighs, or it could refer to something that brightens up a dark room. One word, one pronunciation, two meanings. Words like this are called homonyms, and there are hundreds of them. The word theory is also a homonym.

Young earth creationists use the seventh definition (as listed on dictionary.com), which is “guess or conjecture.” But scientists use the first definition, which is “a coherent group of tested general propositions, commonly regarded as correct, that can be used as principles of explanation and prediction for a class of phenomena.” In science, a theory is as good as it gets. There is nothing higher. Scientists make observations, develop hypotheses, test them, discover laws, and construct theories which explain those laws. A scientific theory is not even in the same ballpark as a mere guess.

One important feature of a scientific theory is that it can make very specific predictions. So for example, someone could say, “If the general theory of relativity is true, we should be able to predict exactly how much a star’s light will bend as it moves through the sun’s gravitational field, and we can confirm this prediction during a solar eclipse.” That is exactly what happened. Someone could also say, “If the theory of evolution is true, we should be able to dig in rock from the late Devonian river sediments and find a transitional fossil between lobe-finned fish and the earliest known tetrapods.” This also happened.

Now try naming some specific predictions made by young earth creationists. And I don’t mean vague predictions that anyone could pull out of their ass such as, “If Noah’s flood were true you would expect to find millions of dead things buried in rock layers.” (No shit, Sherlock! Did you notice that prediction fits with evolution, too?) I’m talking about a prediction that would only be true of the theory in question. Something we can measure or something we can go find. Can’t think of anything? Don’t blame yourself. Creationism doesn’t make predictions like these because it’s not a theory in the scientific sense. It’s the type of theory creationists mistakenly accuse evolution of being: a “guess or conjecture.”

Another important feature of a scientific theory is falsifiability, which means there’s at least one way to try and prove it wrong. For example, there are many ways you could prove evolution wrong: a transitional fossil in the wrong layer of rock, an animal that doesn’t share DNA with any other animal, or a crocoduck. (That’s right, Kirk Cameron, you numbnut. A crocoduck would actually disprove evolution). Most scientists would love to disprove evolution because it would win them a Nobel Prize. But after 150 years, it still hasn’t been done. What does that tell you?

Now I suppose young earth creationism is partly falsifiable because scientists have definitely proved the earth is not young. But the concept of god is not falsifiable, and that’s a big problem. Here’s an illustration that explains why: Let’s say I tell you, “Somewhere in the Andromeda galaxy there is a planet full of pink penguins.” What test could potentially prove that statement false? There isn’t one. We can’t possibly travel billions of light years and check billions of planets, so the idea is completely useless in the scientific sense.

Now back to Earth: We still don’t know exactly how life formed in the first place, so creationists like to say, “God did it.” Again, what test could potentially prove that statement false? I could just as easily say “aliens did it” or “the devil did it.” Go ahead, try to prove me wrong. Even if scientists did figure out the mechanism by which life came into existence, creationists would just say, “Yea, but God made that happen.” And I could just say, “No, the tooth fairy made that happen.” If your idea is not falsifiable, then it’s not a scientific theory. It’s not even a hypothesis!

To all young earth creationists: If evolution is just a theory (by which you mean guess), explain how hundreds of thousands of scientists from many different fields have all found data that confirm it. If scientists are just making this up as they go, you would expect there to be many different explanations for the diversity of life (just like there are many different creation stories). Instead, well over 99% of scientists are in complete agreement about the basics of evolutionary theory. How can that be? It’s not like there’s a science pope who tells them what they’re supposed to believe. Maybe it’s because evolution isn’t just a theory.

If you still think evolution is just a theory, what about atomic theory, or germ theory, or quantum theory? Maybe nuclear power is a hoax, maybe germs don’t cause disease, maybe none of our electronics actually work since quantum theory is just a theory. Are you starting to get it, yet? If you’re going to keep misusing that word, then you may as well stop listening to music since music theory is just a theory. Do I sound ridiculous? Imagine how ridiculous you sound to me.